So it looks like the nvidia driver has been install (it is listed in kernel modules) but not it is not used... I found it also weird that lspci does not give me any "Kernel driver in use" for the VGA controller...

I did not want to give the impression that I followed blindly some instruction list... I just wanted to give you the an enumeration of the actions I performed on a freshly installed centos 7.5 since I have few expresses with installing NVIDIA drivers on centos.

I installed Bumblebee in order to recover a dektop interface. Without Bumblebee during startup, my screen was stuck at blinking cursor & the very start of centos 7, i can only use command lines with ctrl+alt+f2. With Bumblebee at least I was able to get my Desktop back.

To answer your questions:
1) I reboot after the install --> as mentioned before, without Bumblebee, I got stuck at the centos startup. With Bumblebee I get a functionnal Desktop.
2) I run lsmod --> no trace of nvidia nor nouveau but the snd_hda_codec_XXX is listed (I put the complete output in attachment)
3) I put the complete Xorg.0.log file in attchment.

I did not want to give the impression that I followed blindly some instruction list... I just wanted to give you the an enumeration of the actions I performed on a freshly installed centos 7.5 since I have few expresses with installing NVIDIA drivers on centos.

I installed Bumblebee in order to recover a dektop interface. Without Bumblebee during startup, my screen was stuck at blinking cursor & the very start of centos 7, i can only use command lines with ctrl+alt+f2. With Bumblebee at least I was able to get my Desktop back.

To answer your questions:
1) I reboot after the install --> as mentioned before, without Bumblebee, I got stuck at the centos startup. With Bumblebee I get a functionnal Desktop.
2) I run lsmod --> no trace of nvidia nor nouveau but the snd_hda_codec_XXX is listed (I put the complete output in attachment)
3) I put the complete Xorg.0.log file in attchment.

Thank you very in advance for your help.

Best regards.

This is all very confusing. IF this is a DESKTOP system, try removing the installed graphics card. If there are two graphics card try removing one. if there is only one card try relocating to another slot. Regardless make sure that this is an NVIDIA card to start with and then go to the Nvidia website to confirm what classification it belongs under. You should NOT have to use Bumblebee with a desktop system.

Next what are you using for a Desktop Environment?? KDE, GNOME, GNOME "Classic", etc.? For fun try installing KDE (if you are not already using it). In short try an alternate DE and see if the problem still exists. What this almost sounds like is a problem with GDM, try replacing GDM with LightDM . To install LightDM see this post:

There is something really wrong here: Either your graphic card is improperly identified and you have the wrong driver; you are using a DE that might be unrecognized; or this is a problem with your Display Manager (GDM) which might be solved by switching to another DM light LightDM. Any or all of these might be what is causing your problem.